Imaging system

ABSTRACT

A process and device for removing grit and other foreign matter from the toner in an electrostatic developing apparatus, where its presence may harm the electrostatographic layer or cause other deleterious effects. The electrostatographic surface is charged in the usual manner in one area, which is to record the picture, and another area, the terminal area of the first area, is charged to an opposite polarity. During the operation of the machine, grit and other foreign matter will be attracted to the latter area.

United States Patent lnventor Robert W. Madrid [56] References Cited A l N g ag UNITED STATES PATENTS PP Filed Dec 1969 2,911,330 11/1959 Clark 355/15 X Patented Oct. 5, 1971 Primary Examiner-John M. Horan Assignee Xerox Corporation Attorneys-James J. Ralabate, Albert A. Mahassel, Peter H.

Rochester, N.Y. Kondo and William Kaufman ABSTRACT: A process and device for removing grit and other foreign matter from the toner in an electrostatic g Fi developing apparatus, where its presence may harm the elecraw trostatographic layer or cause other deleterious effects. The U.S. Cl 355/17, electrostatographic surface is charged in the usual manner in 209/127 one area, which is to record the picture, and another area, the Int. Cl. B03e 7/08 tenninal area of the first area, is charged to an opposite polari- Field of Search 355/3, 17; ty. During the operation of the machine, grit and other foreign 209/ 1 27, 129 matter will be attracted to the latter area.

:5 o I] 3, Q ll 6 0 g V a o I o 4 ut r c x 33 k a v 8/ 0 PATENTED UN 5 IBYI SHEET 1 OF 3 a W Wash 9% INVENT OR. ROBERT W. MADRID ATTORNEY PATENTEDBCI 5l97l SHEET 3 OF 3 INVIiN'I'OR. ROBERT W. MADRID ATTORNEY IMAGING SYSTEM This invention relates to electrostatography. More particularly, this invention relates to improvements in electrostatographic processes andapparatus whereby grit can be removed from the developer thereby reducing unsightly deposition in noncharged areas.

In a typical electrostatographic process, for example, as disclosed in Carlson Pat. No. 2,297,691, issued Oct. 6,1942, an electrostatographic imaging surface comprising a layer of photoconductive insulating material on an electrically conductive backing is given a uniform electrostatic charge over its surface and is then exposed to the subject matter to be reproduced, usually by conventional-projection techniques. This exposure'discharges the imaging surface in image configuration and thereby creates an electrostatic latent image on or in the photoconductive layer. Development of the latent image is effected with an electrostatically charged finely divided material, such as an electroscopic powder, that is brought into surface contact with the photoconductive layer and is held thereon electrostatically in a pattern corresponding to the electrostatic latent image. Thereafter, the developed powder image is usually transferred to a transfer support surface for example, paper, to which it may be affixed by any suitable means.

The cascade method of latent image development has found extensive commercial acceptance and generally consists of gravitationally flowing across the electrostatographic surface a two component developer material consisting of an electroscopic marking powder termed toner and a granular material called carrier which consists preferably of spherical particles devoid of so-called grit which includes fine chips, powder, filaments and dust which may freely reside in the carrier mixture or adhere tenaciously to the surface of individual carrier beads.

Illustrative examples of such two component developer materials are disclosed in Walkup et a]. Pat. 2,638,416; Walkup Pat. No. 2,618,551; Wise Pat. No. 2,618,552 and Copley Pat. No. 2,659,670. Generally carrier particles are much larger relative to the toner particles, toner particles generally having an average particle diameter between about 1 and 30 microns; whereas the carrier particles, for example, may have an average particle diameter from about 50 to 700 microns.

As indicated in the aforementioned patents, conventionally the carrier particles act as vehicles to carry toner to latent image areas and serve to triboelectrically charge toner so that toner may be pulled off of the carrier particles to image areas but not to background areas. Carrier beads also pick up toner particles which might tend to adhere to uncharged or background areas.

The accumulation of grit in the developer is to be avoided since grit can be deposited on the electrostatographic surface and remain thereon after development and be carried through subsequent image transfer and cleaning steps. Grit on the imaging surface during the image transfer step prevents intimate contact of said surface with the transfer support surface in the region of the grit thus causing incomplete image transfer in that region. Also pressure is often required during this transfer step and this pressure may cause grit to scar, dent or otherwise degrade the relatively delicate electrostatographic imaging surface.

Alsoin automatic recyclable electrostatographic copying machines the imaging surface is generally cleaned after the transfer step to ready said surface for a new imaging cycle. In the cleaning step where any remaining toner is removed from the imaging surface to ready it for reuse, especially where web beltsin skidding contact with said surface are employed as the cleaning means, grit on the imaging surface, being ground against it, may cause serious damage to said surface which ordinarily should be very smooth to produce quality prints.

In addition, it is found that grit which adheres to the surface of both round and irregular carrier beads can cause unsightly deposition in noncharged background areas of the imaging surface. To require remedial'measures such as tapping or air .pressureto remove grit from the imaging surface after the development step would add greatly to the complexity of such apparatus. This problem will become even more acute as developers with greater longevity are obtainedThe very nature of the developer system is a grinding action; consequently, a certain amount of grit will always be produced in any system employed. No method, however, has heretofore been found which satisfactorily continuously removes grit from the bead surface.

Accordingly, it is an object of the present invention to provide a process for continuously removing grit from the developer system.

It is another object of the present invention to provide apparatus adapted to continuously remove grit from the developer system.

It is still another object to provide means for reducing the occurrence of grit on the electrostatographic imaging surface thereby reducing potential damage thereto.

These as well as other objects are accomplished in the present invention which, in one embodiment, provides a process for electrostatographic reproduction with continuous removal of grit from the developer comprising:

a. electrostatically charging the major portion of an electrostatographic imaging surface with a charge of first polarity and at least one terminal portion of said surface with a charge of relatively opposite polarity to that being imposed upon said major portion of said surface;

b. imaging the major portion of said surface to impart a latent electrostatic image thereto while substantially precluding the charge on said terminal portion of said surface from being discharged;

c. cascading developer across the entire surface whereby the latent image on the major portion of said surface is developed and grit is selectively attracted to said terminal portion of said surface. I

Thereafter, depending upon the type of electrostatographic process employed, the developed image can be recovered or the developer can be transferred in image configuration to a support web and the entire electrostatographic surface can thereafter be cleaned thereby removing the attracted grit and any developer remaining on said surface. 7

In another embodiment, an improved electrostatographic reproducing apparatus adapted to continuously remove grit is provided comprising:

i) an electrostatogaphic imaging surface;

ii) at least two corona discharge electrodes spaced from said surface and extending transversely across the surface thereof; the first corona discharge electrode extending across a major portion of said surface and adapted to impose a charge upon said portion of said surface, and at least one additional corona discharge electrode extending across at least one terminal portion of said surface and adapted to impose a charge thereon of relatively opposite polarity to that imposed by said first electrode;

iii) shielding members affixed to a frame element of the electrostatographic reproducing apparatus adapted to segregate said major and terminal portions of said imaging surface with respect to incident light and electrostatic charge;

iv) means for cascading developer across the entire imaging surface;

v) means for recovering said developer upon completion of its traverse of said surface; and

vi) means for cleaning the entire imaging surface to remove attracted grit and any residual developer therefrom.

It has now been found that grit which is obtained primarily by abrasion within the developer system as it cascades over the electrostatographic imaging surface includes fine chips, powder, filaments, and dust, derived primarily from the carrier, exhibits essentially the same charge as that of the carrier. Accordingly, by imposing an electrostatic charge on the electrostatographic surface relatively opposite to that of the accumulated grit in the developer, a charge differential is created which enables the grit to be selectively removed from the developer system.

For a better understanding of the invention, reference is made to the following detailed description of the invention to be read in conjunction with the accompanying drawing, wherein:

FIG. 1 illustrates schematically an electrostatographic apparatus adapted to be employed in accordance with the invention;

FIG. 2 is a schematic partial perspective view of the charging, imaging, developing and cleaning stations in accordance with one embodiment of the invention;

FIG. 3 is a schematic partial perspective view of the charging, imaging, developing and cleaning stations in accordance with another embodiment of the invention;

FIG. 4 is an isolated schematic partial perspective view of the cleaning and charging stations illustrating a further embodiment of the present invention;

FIG. 5 is a schematic, partial perspective view of the charging, developing and cleaning stations illustrating use of a slave roll.

As shown schematically in FIG. 1, an automatic electrostatographic reproducing apparatus comprises an electrostatographic imaging surface including a photoconductive layer or light-receiving surface on a conductive backing and formed in the shape of a drum, which is mounted on a shaft 15 joumaled in a frame to rotate in the direction indicated by the arrow to cause the imaging surface sequentially to pass a plurality of electrostatographic processing stations.

The several electrostatographic processing stations in the path of movement of the drum surface may be described functionally, as follows:

A charging station at which a corona discharge device imparts a uniform electrostatic charge to the major portion of the photoconductive layer of the imaging surface and at least one other corona discharge device imposes a uniform electrostatic charge of relatively opposite polarity to at least one terminal portion of the photoconductive layer of said surface;

An exposure station at which a light or radiation pattern of copy to be reproduced is projected onto the major portion of the imaging surface to dissipate the charge in the exposed areas thereof and thereby fonn a latent electrostatic image of the copy to be reproduced;

A developing station, at which a developing material, including toner particles having an electrostatic charge opposite to that of the electrostatic latent image, are cascaded over the entire imaging surface whereby the toner particles adhere to the electrostatic latent image to form a powdered image in the configuration of the copy being reproduced. Any accumulated grit in the developer material is selectively attracted to the oppositely charged terminal portion(s) of the imaging surface thereby being continuously selectively removed during the development of the latent image;

A transfer station, at which the developer is electrostatically transferred in image configuration from the imaging surface to a transfer material or support surface; and

A cleaning and discharge station at which the entire imaging surface is brushed to remove the attracted grit and residual toner particles remaining thereon after image transfer and at which the major portion of the imaging surface is exposed to a relatively bright light source to effect the substantially complete discharge of any residual electrostatic charge remaining thereon.

The charging station is preferably located as indicated by reference character A. As shown, the charging arrangement includes a corona charging device 21 which includes a corona discharge array of one or more corona discharge electrodes that extend transversely across the major portion of the imaging surface and are energized from a high potential source and are substantially enclosed within a shielding member. In addition, at least one other corona charging device 31 is spaced from said imaging surface and extends transversely across either or both the terminal portions thereof in substantially the same radial plane as said corona charging device 21 and is energized from a high potential source of opposite polarity to that of corona charging device 21. If desired, corona charging device 21 can be shielded from corona charging device 3| with respect to incident light and electrostatic charge such as by shielding member 33.

Next subsequent thereto in the path of motion of the electrostatographic imaging surface is an exposure station B. An optical scanning or projection system is provided to project a flowing image onto only the major portion of the imaging surface, i.e., that portion of the surface charged by corona charging device 21, from a stationary original.

The optical scanning or projection assembly comprises a stationary copyboard which consists of a transparent platen member 22 such as, for example, a glass plate or the like, positioned on the exterior of the cabinet which is adapted to support a document to be reproduced, the document being uniformly illuminated and arranged in light projecting relation to the moving light receiving electrostatographic imaging surface. Uniform lighting is provided by banks of lamps LMPS arranged on opposite sides of the copyboard. Scanning of the document on the stationary copyboard is accomplished by means of a mirror assembly which is oscillated relative to the copyboard in timed relation to the movement of the imaging surface.

The mirror assembly which includes an object mirror 23, is mounted below the copyholder to reflect an image of the document through a lens 24 onto an image mirror 25 which, in turn, reflects the image onto the major portion of the imaging surface through a slot in a fixed light shield 26 positioned adjacent to the imaging surface. The shielding member 33 between corona charging device 21 and corona charging device 31 precludes the charge on said terminal portion(s) of the electrostatographic imaging surface from being discharged during exposure of the major portion of said surface.

Adjacent to the exposure station is a developing station C in which there is positioned a developer apparatus 30 including a casing or housing having a lower or sump portion for accumulating developer material. A bucket type conveyor 48 is used to carry the developing material to the upper part of the developer housing where it is cascaded over a hopper chute 50 onto the entire surface of the imaging surface, i.e., both the major and terminal portions thereof, to effect simultaneous development on the major portion of said surface and selective cleaning of the developer to remove accumulated grit therefrom on the terminal portion(s) of said surface. A toner dispenser 35 is used to accurately meter toner to the developer material as toner particles are consumed during the developing operation.

Positioned next and adjacent to the developing station is the image transfer station D which includes a sheet feeding arrangement adapted to feed sheets of support material, such as paper or the like, successively to the drum in coordination with the presentation of the developed image on the major portion of the drum surface at the transfer station.

The sheet feeding mechanism includes a sheet feed device 40 adapted by means of vacuum feeders to feed the top sheet of a stack of sheets on the tray 41 to rollers 42 cooperating with the belts of paper transport 44 for advancing the sheets sufficiently to be held by paper transport 44 which, in turn, conveys the sheet to a sheet registration device 45 positioned adjacent to the imaging surface. The sheet registration device rests and aligns each individual sheet of material and then in timed relation to the movement of the imaging surface, advances the sheet material into contact with the major portion of said surface in registration with a previously formed powder image on said portion of the imaging surface.

The transfer of the developer in image configuration from the imaging surface to the sheets of support material is effected by means of a corona transfer device 51 that is located at or immediately after the line of contact between the support material and the rotating drum. In operation, the electrostatic field created by corona transfer device 51 is effective to tack the support material electrostatically to the major portion of the imaging surface while in contact therewith. Simultaneously with the tacking action, the electrostatic field is effective to attract the toner particles comprising the powder image from the imaging surface and cause them to adhere electrostatically in image configuration to the surface of the support material.

Immediately subsequent to the image transfer station there is positioned a stripping apparatus comprising a paper pickoff mechanism 52 for removing the sheets of support material from the imaging surface. This device, which can be of the type disclosed in Rutkus et al. US. Pat. No. 3,062,536, includes a plurality of small diameter orifices supplied with pressurized aeriform fluid by a suitable pulsator or other device. The pulsator is adapted to force jet pressurized aeriform fluid through the outlet orifices into contact with theimaging surface slightly in advance of the sheet of support material to strip the leading edge of the sheet from said surface and'to direct it onto an endless conveyor 55 where the sheet material is carried to a fixing device 60. At the fixing device, the transferred powder image on the sheet of support material is per manently fixed or fused thereto as by heat. After fusing, the reproduction is discharged from the apparatus at a suitable point for collection external of the apparatus by means of the conveyor 65. In the embodiment shown, the reproductions are discharged form conveyor 65 into a receiving tray 61.

' The next and final section in the device is an imaging surface cleaning station E,'having positioned therein a corona preclean device 66, an imaging surface cleaning device 70, adapted to remove the attracted grit and any powder remaining on the imaging surface after transfer by means of a rotating brush 75, and a discharge lamp LMP-l adapted to flood the imaging surface with light to cause dissipation of any residual electric charge remaining on said surface.

To remove the attracted grit from the terminal portion(s) of the imaging surface and any residual powder from the major portion of said surface, there is disposed a cylindrical brush 75 rotatably mounted on an axle and driven by a motor, not shown. For collecting the grit and powder particles removed from the imaging surface by the brush, there is provided a hood 73 that is formed to encompass the brush area. To ensure thorough cleaning of the brush, a flicking bar 74 is secured to the interior of the dust hood and in interfering relation with the ends of the brush bristles whereby dust and grit particles may be dislodged therefrom.

For removing dust particles and grit from the brush and hood, an exhaust duct 76 is arranged to cover the outlet of the hood, the exhaust duct being connected at its other end to the wall of a filter box 77 attached to the hood. A filter bag 78 is secured within the filter box with the mouth of the filter bag in communication with the exhaust duct. Motor fan unit MOT connected to the filterbox, produces a flow of air through the filter box drawing air through the area surrounding the imaging surface and the hood, the air entrained powder and grit particles removed from the imaging surface by the brush as the air flows through the dust hood. Powder and grit particles are separated from the air as it flows through the filter bag so that only clean air reaches the motor unit.

Suitable drive means are provided to drive the imaging surface, rotating mirror and sheet feeding mechanism at predetermined speeds relative to each other, and to effect operation of the bucket-type conveyor and toner dispenser mechanism and the other operating mechanisms.

In the embodiment of the present invention shown in FIG. 2, two corona discharge electrodes 21 and 31 are spaced from the electrostatographic imaging surface and extend transversely across said surface in substantially the same radial plane. It is not considered critical, however, that said discharge electrodes be in the same radial plane. Corona discharge electrode 21 extends across a major portion of the imaging surface, i.e., across about 75 percent to about 99 percent of said surface and is adapted to impose a charge of a given polarity upon said portion of the imaging surface. The major portion of the imaging surface is employed in the conventional manner for forming an electrostatic latent image. In order for the terminal portion of the imaging surface to be employed in accordance with the present invention for continuous grit removal and yet not impinge upon the area of the said surface available for reproduction, the imaging surface can be extended, if desired, in the axial direction to enlarge the imaging surface to from about 1 percent to about 25 percent beyond the normal length thereof. In this manner, the area available for reproduction remains the same.

Alternatively, as shown in FIG. 5, a slave roll 17 can be mounted on either or both ends of the shaft 15 supporting the imaging surface 20 and, if desired, through appropriate gear reduction (not shown) can be adapted to rotate at a relatively slower rate as compared to the imaging surface 20. The slave roll 17 can be manufactured from a reusable photoresponsive material such as selenium or can be a nonreusable photoresponsive material and periodically replaced as, for example, employing a roll covered by zinc oxide coated paper. Although not considered necessary, the slave roll 17 preferably is run at from about 10 percent to about 50 percent of the rate of speed of the imaging surface 20. In this manner, grit removal is efficiently accomplished on the slave roll 17.

If the imaging surface 20 is extended or a slave roll employed, the hopper chute 50 from within which the developer is cascaded over the imaging surface and the rotating brush 75 must be similarly enlarged in order to obtain a cascade of developer across the entire length of the imaging surface or the imaging surface and the slave roll(s) and to remove the attracted grit from the terminal portion of the imaging surface or the slave roll(s), as well as any retained powder from the major portion of said imaging surface.

Corona discharge electrode 21 is adapted to impose a charge of fixed polarity upon the major portion of the imaging surface. Corona discharge electrode 31 is adapted to impose a charge on the terminal portion of said imaging surface or the slave roll(s) relatively opposite in polarity to that imposed upon the major portion of said imaging surface. The discharge electrodes 21 and 31 are shielded from each other by shielding member 33 affixed to a frame element and extending between said electrodes. Shielding member 33 serves to prevent incident light from discharging the electrostatic charge imposed upon the imaging surface and also prevents cancellation of the desired electrostatic charge by precluding interaction of the charges of opposite polarity emanating from the proximately situated electrodes. Shielding member 33 can extend through both the charging and exposure stations A and B thereby insuring that a charge is retained upon the terminal portions of the imaging surface or the slave roll relatively opposite in polarity to that imposed upon the major portion of the imaging surface and is not discharged upon exposure of said major portion of Said surface.

In FIG. 3, an alternative embodiment of the present invention is illustrated. Corona discharge electrode 21 extends across the major portion of the electrostatographic surface 20 and is flanked on both sides by corona discharge electrodes 3] and 31' extending across both terminal portions of said surface. Similarly, of course, discharge electrodes 31 and 31' can extend over the slave roll(s) as described herein. Electrodes 31 and 31 are adapted to impose an electrostatic charge upon both terminal portions of the imaging surface or upon slave rolls opposite in polarity to that imposed by electrode 21 upon the major portion of the imaging surface. Interposed between; said electrodes are shielding members 33 and 33. Shielding members 33 and 33' are attached to a frame element of the apparatus and can extend through both charging and exposure stations A and B.

In order to retain the conventional surface area of the imaging surface 20 available for reproduction purposes, the terminal portions thereof can each be extended to from about 1 percent to about 25 percent beyond the conventional length of said imaging surface. Similarly, slave rolls having the same diameter as the imaging surface 20, and lengths equivalent to from about 1 percent to about 25 percent of the conventional length of said imaging surface can be employed. Since grit accumulation in the developer is a gradual phenomenon, the

the slave rolls can be varied widely and can, if desired, be

more or less than extensions of from about 1 percent to about 25 percent. Preferably, and in order to conveniently embody the present invention in existing equipment, extensions of the imaging surface or use of slave rolls having lengths of from about 1 percent to about 5 percent of the conventional length of the imaging surface are most preferred.

F IG 4 illustrates a further and preferred embodiment of the present invention wherein the drum cleaning station E comprises a corona preclean device consisting of a corona discharge electrode 66 extending over a major portion of the imaging surface having a polarity opposite to that of discharge electrode 21 and a second discharge electrode 66' extending over the terminal portion of the imaging surface having a polarity opposite to that of discharge electrode 31. Electrodes 66 and 66 can be shielded from each other by shielding member 67 affixed to a frame element and extending between said electrodes to prevent dissipation of the charges imposed by said electrodes upon the imaging surface. Preclean electrodes 66 and 66 charges on the major and terminal portions of the imaging surface opposite to that imposed by charging electrodes 21 and 31 which act to loosen any powder adhering on the major portion of the imaging surface after the transfer operation and any attracted grit on the terminal portion of said surface by neutralizing the charge on said powder or grit. The loosened powder and grit can then be easily removed by rotating brush 75 extending across the entire imaging surface. Discharge lamp LMP-l can thereafter flood the imaging surface with light causing dissipation of any residual electric charge remaining on the imaging surface before the cycle is renewed. Of course, preclean electrode 66' can be situated above both terminal portions of the drum to neutralize the charges imposed in the embodiment shown in FIG. 3. Similarly, said electrode 66' can be situated over slave rolls to neutralize the charges thereon.

, The present invention can be employed with any imaging surface, including any suitable photoconductive surface. Well known photoconductive materials include vitreous selenium, selenium alloys, organic or inorganic photoconductors imbedded in a nonphotoconductive matrix, organic or inorganic photoconductors imbedded in a photoconductive matrix, or the like. Representative patents in which photoconductive materials are disclosed in U.S. Pat.,NO. 2,803,542 to Ullrich, U.S. Pat. No. 2,970,906 to Bixby, U.S. Pat. No. 3,121,006 to Middleton, and U.S. Pat. No. 3,151,982 to Corrsin. Reusable photoreceptor surfaces comprising vitreous selenium, selenium alloys or selenium mixtures are preferred because their faster photographic response allows higher machine speeds to be obtained.

The photoconductive insulating material may be employed alone or dispersed in a high electrical resistance binder. Typical photoconductive insulating materials which may be used without a binder include: vitreous selenium, sulfur, anthracene, and mixtures thereof. Typical photoconductive materials which may be employed in an insulating binder include: sulfur, vitreous selenium, amorphous alpha monoclinic selenium, zinc sulfide, zinc oxide, zinc cadmium sulfide, zinc magnesium oxide, cadmium selenide, cadmium sulfide, zinc silicate, calcium-strontium sulfide, indium trisulfide, gallium triselenide, arsenic disulfide, arsenic trisulfide, arsenic triselenide, antimony trisulfide, cadmium sulfoselenide, doped calcogenides of zinc and cadmium (O,S,Se,Te), aluminum oxide, bismuth oxide, molybdenum oxide, lead oxide, molybdenum iodide, molybdenum selenide, molybdenum sulfide, molybdenum telluride, aluminum iodide, aluminum selenide, aluminum sulfide, aluminum telluride, bismuth iodide, bismuth selenide, bismuth sulfide, bismuth telluride, cadmium telluride, mercuric selenide, mercuric telluride, lead iodide, lead selenide, lead sulfide, lead telluride, cadmium arsenide, lead chromate, gallium sulfide, gallium telluride, indium sulfide, indium selenide, indium telluride, read lead (Pb,O triphenyl amine, 2,4-bis(4,4'- diethylaminophenyl)-l,3,4-oxadiazole, N-isopropylcarbazole triphenylpyrrole, 4,5-diphenylimidazolidinone, 4,5-diphenylimidazolidinethione, 4,5- bis(4'-amlno-phenyl)-imidazolidinone, 1,5-cyanonaphthalene, I ,4-dicyanonaphthalene, aminophthalodinitrile, nitrophthalidinitrile, 1,2,5 ,6-tetraazacyclooctatetraene- (2,4,6,8), 3,4-di(4'-methoxy-phenyl)-7,8-diphenyl l,2,5,6- tetraazacyclooctatetraene-(2,4,6,8), 3,4-di-(4'- phenoxyphenyl)-7,8-diphenyl-1,2,5 ,6-tetraazacyclooctatetraene- (2,4,6,8 3,4,7,8-tetrameth0xyl ,2,5 ,6-tetraazacyclooctatetraene-(2,4,6,8), Z-mercapto-benzthiazole, 2-phenyl-4- alpha-naphthylideneoxazolone, 2-phenyl-4-diphenylidene-ox azolone, 2-phenyl-4-p-methoxybenzylidene-oxazolone, 6- hydroxy-2-phenyl-3-(p-dimethylaminophenyl)-benzofurane,

6hydroxy-2,3-di(p-methoxyphenyl)-benzofurane, 2,3,5,6- tetra-(p-methoxyphenyl)-furo-(3,2)-benzofurane, 4- dimethylamino-benzylidene-benzhydrazide, 4-

dimethylaminobenzylideneisonicotinic acid hydrazide, furfurylidene-(Z)-4'-dimethylamino-benzhydrazide, S-benzilidene-amino-acenapthene, 3-benzylidene-amino-carbazole, (4-N,N-dimethyl amino-benzylidene)-p-N,N- dimethylaminoaniline, (Z-nitro-benzylidene)-p-bromoaniline, N,N-dimethyl-N-(2-mitro-4-cyanobenzylidene)-pphenylenediamine, 2,4-diphenyl-quinazoline, 2-(4- aminophenyl)-4-phenyl-quinazoline, 2-phenyl-4-(4- dimethylaminophenyl)- 7-methoxyquinazoline, 1,3-diphenyl tetrahydroimidazole, l,3-di-(4-chlorophenyl)- tetrahydroimidazole, 1,3diphenyl-2-(4'-dimethyl amino phenyl)-tetrahydroimidazole, 1,3-di-(p-tolyl)-2-(quinol-2-yl)- tetrahydro-imidazole, 3-(4'-dimethylamino-phenyl)-5-(4"- methoxyphenyl )-6-phenyll ,2,4-triazine, 3-pyridyl-( 4 dimethylaminophenyl )-6-phenyl-l ,2,4-triazine, 3-(4 aminophenyl)-5,6-diphenyl l ,2,4-triazine, 2,5-bis [4- aminophenyl-(l')]-3,4-triazole, 2,5-bis [4'N-ethyl-N-acetylamino-phenyl-( l l ,3,4-trizole, 1,5-diphenyl-3-methylpyrazoline, 1,3,4,5-tetraphenylpyrazoline, l-phenyl-B-(pmethoxy-styryl)-5-(p-methoxyphenyl)-pyrazoline, 2-(4,'- dimethylamino phenyl)-benzoxazole, 2-(4'-methoxyphenyl)- benzthiazole, 2,5-bis-[p-amino-phenyl-( l )]-1,-3,4-oxadiazole, 4,5-diphenyl-imidazolone, S-amino-carbazole, and mixtures thereof.

Any suitable high resistance binder may be employed to suspend the photoconductive material. A film-forming binder material having a relatively high dielectric constant and high dielectric strain is preferred. Typical film-forming materials include: polyolefins such as polyethylene, polypropylene and chlorinated polyethylene; vinyl and vinylidene resins such as polystyrene, polyvinyl pyrrolidone, acrylic polymers, polyvinyl acetate, polyvinyl butyral, and polyvinyl chloride; fluorocarbons such as polytetrafluoroethylene and polychlorotrifluoroethylene; styrene-butadiene, heterochain thermoplastics such as polyamides, polyesters, and polycarbonates; phenolic resins such as phenol-formaldehyde and resorcinol-formaldehyde; melamine formaldehyde resins such as methylol melamine resins, dimethyl trimethylol melamine resins, and trimethylol melamine resins; silicone resins; epoxy resins; and mixtures thereof. Any suitable additives such as emulsifiers, wetting agents, pH regulators, brightening agents and stabilizers may be admixed with the film-forming binder.

In accordance with the present invention, at least one terminal portion of the electrostatographic imaging surface or a slave roll is electrostatically charged with a charge relatively opposite to that of the accumulated grit in the developer. For example, in the conventional electrostatographic copying operation, toner is generally charged negatively in relation to its positive carrier so that it will be attracted to the positive charged areas of the electrostatographic imaging surface. Heretofore, if fragments of the carrier as minute chips coated and uncoated with toner came in contact with the photoreceptor they deposited mainly in the background areas (near zero charge). in accordance with the-present invention, however, the tenninal portion(s) of the imaging surface or a slave roll is charged negatively while the major portion of said surface is charged positively and therefore, said terminal portion or the slave roll has a greater affinity for the positive or mixed polarity agglomerates forming the grit. lf, however, a reversal system is employed where the toner is relatively positive in relation to the carrier, a positive charge would be required on the terminal portion (s) of the imaging surface or slave roll to remove the more negatively charged grit.

The present invention can be conveniently incorporated in conventional electrostatographic reproduction apparatus. For purposes of illustration only, the invention has been described with respect to the type of reproducing apparatus shown in FIG. 1. It should be apparent, however, that the present invention is amenable to any electrostatographic reproduction system involving a cascade type developer.

The present invention can be employed, for example, in processes and apparatus which do not involve a rotating drum but instead rely upon the use of nonreusable photoresponsive surfaces; such as, for example, zinc oxide binder paper or phthalocyanine binder paper. By extending the width of conventional zinc oxide paper or by using a slave roll carrying zinc oxide paper and employing the process and apparatus of the present invention, the grit is continuously attracted to the terminal portions, i.e., margins of the paper or to the paper on the slave roll. By slitting and discarding the margins of the paper, or by periodically discarding the paper on the slave roll, the attracted grit is conveniently discarded.

The following examples further specifically define, describe and compare the grit removal techniques of the present invention. All parts and percentages are by weight unless otherwise indicated. The examples below are intended to illustrate various embodiments of the continuous cleaning cycles of the present invention and are not intended to limit the scope or spirit of the invention.

ln the following examples, the grit level generated through use of the developer system was determined as follows:

'A sample of the developer system being evaluated is removed from the development station of an automatic recyclable electrostatographic copying machine and is charged to a Faraday Cage which has been previously weighed. The loaded Faraday Cage is reweighed to determine the sample weight. The Cage terminates at opposite ends thereof in 250 micron screens, each about one inch in diameter. At one end of the cage, a glass tube about 1 foot in length and about 3 inches in diameter connects one of the 250 micron screens with a 30 micron screen.

A blast of air is sent through the cage causing toner and grit to be separated from the carrier and to pass through the glass tube. The carrier particles are retained in the cage by the 250 micron screen. Suction is applied to the 30 micron screen causing all particles less than 30 microns to pass through. Particles greater than 30 microns in size are considered as grit. The grit particles are retained on the 30 micron screen. The cage is weighed after the air blast to determine the total amount of toner and grit blown off. The 30 micron screen is weighed to determine the amount of grit. The ratio of the grit on the 30 micron screen to the total weight of toner and grit blown off is considered the amount of grit in the sample. The grit level can then be determined by the following relationship:

Grit level grit weight total blowoff weight of toner and grit X l EXAMPLE 1 Control: A developer system comprising 600 micron flint shot having a percent coating thereon of ethyl cellulose toned to 1 percent with a toner comprising a styrene-n-butyl 3600 Xerox copier. The copier is operated in conventional manner for 70,000 copies. The grit level is 1.26 percent after 10,000 copies and increases to 3.09 percent after 70,000 copies.

For purposes of comparison, the copier is modified so that the electrostatographic imaging surface is laterally extended by extending the terminal portions of the imaging surface 2 inches on each side. Also, the hopper chute in the developer station and the rotating brush in the cleaning station are similarly extended. in addition, two corona charging devices are situated adjacent the terminal portions of the conventional corona charging device and extend across the extended terminal portions of the imaging surface. These corona charging devices are energized from a high potential source of opposite polarity to that of the conventional corona device situated over the major portion of the imaging surface. Shielding barriers are interposed between the respective corona discharge devices extending into close proximity with the imaging surface to prevent interaction and/or dissipation of the opposite charges imposed upon the terminal and major portions of the imaging surface. With these modifications, the copier is otherwise operated in conventional manner employing the developer system defined above. The major portion of the imaging surface is employed for reproduction purposes whereas the 2- inch terminal portions are continuously employed to selectively remove grit from the developer as it cascades across said terminal portions. Operating in this manner, a grit level of less than 1.26 percent is observed after 70,000 copies.

EXAMPLE 2 This example illustrates the applicability of the present invention to electrostatographic processes employing a nonreusable photoreceptor.

A Bruning magnetic brush copier was modified to employ a developer composition comprising toner particles described in example I and 450 micron steel shot coated with a vinyl chloride copolymer dyed with Luxol Fast Blue dye. A negative charge is imposed on Bruning zinc oxide paper during the reproduction cycle. Operating in this manner, the copier was print tested to 70,000 copies. The grit level at 70,000 copies was double that at l0,000 copies.

For purposes of comparison, the copier is modified to accommodate zinc oxide paper, the width of which is extended 2 inches beyond the width of conventional zinc oxide paper. The development section is similarly extended to enable developer to contact the extended portion of the paper. A corona discharge device is situated adjacent the conventional corona discharge device and extends transversely across the extended portion of the paper. Said corona discharge device is energized from a high potential source of opposite polarity to that of the conventional corona discharge device. immediately prior to the discharge portion of the copier is situated a knife edge slitter adapted to sever the 2-inch extension from the major portion of the paper thereby enabling conventionally sized developed prints to be obtained while simultaneously removing grit from the developer upon the severed marginal portion of the paper. Said severed marginal portion is passed to a windup roll which can be periodically discarded. With these modifications, the copier is otherwise operated in conventional manner employing the developer of example I. The major portion of the zinc oxide paper is employed for reproduction purposes whereas the margin along one side of the paper is continuously employed to selectively remove grit from the developer as it contacts said margin. Operating in this manner, the grit level remains below 1 percent up to the 70,000 copies.

EXAMPLE 3 This example illustrates the use of a reusable photoresponsive slave roll to obtain continuous grit removal.

Control: A developer system comprising 600 micron flint shot having a 10 percent coating thereon of ethyl cellulose toned to 1 percent with a toner comprising a styrene-n-butyl methacrylate copolymer, polyvinyl butyral and carbon black prepared by the method disclosed in example I of U.S. Pat. No. 3,079,342 is charged to the development section of a 3600 Xerox copier. The copier is operated in conventional manner for 70,000 copies. The grit level is 1.26 percent after 10,000 copies and increases to 3.09 percent after 70,000 copies.

For purposes of comparison, the copier is modified by mounting a slave roll on the main shaft supporting the photoresponsive selenium drum conventionally employed as the imaging surface. The slave roll comprises a layer of selenium on a conductive backing formed in the shape of a' drum of the same diameter as the conventional selenium drum and 2 inches wide. Through proper gear reduction, the slave roll is adapted to rotate at 0.25 linear inch per minute whereas the conventional selenium drum rotates at about 1.45 linear inches per minute. A corona charging device is situated above the slave roll and is energized from a high potential source of opposite polarity to that of the conventional corona charging device situated above the selenium drum. The slave roll and its corona charging device are optically isolated from the selenium drum and its corona charging device by barrier shields to prevent interaction and/or dissipation of the opposite charges imposed upon the drum and slave roll. The development and cleaning stations are commensurately extended to accommodate cascading developer over the slave roll and removing the grit selectively attracted thereto. With these modifications, the copier is otherwise operated in conventional manner employing the developer system defined in example 1. The selenium drum is used in conventional manner for reproduction purposes whereas the slowly rotating, oppositely charged slave roll continuously selectively removes grit from the developer. Operating in this manner, the grit level remains below 1.26 percent up to 70,000 copies.

EXAMPLE 4 Control: A Bruning copier is print tested to 70,000 copies using Bruning zinc oxide paper and the developer of example 2. The grit level increases from 1.02 percent at 10,000 copies to 2.04 percent at 70,000 copies.

For purposes of comparison, the copier is modified by mounting a first slave roll in the main shaft supporting the zinc oxide paper feed roll. Similarly, a second slave roll is mounted on the shaft supporting the drum over which the zinc oxide paper containing a latent electrostatic image is passed for magnetic brush development. The first roll is driven at the same speed as the paper feed roll whereas the second roll is idle. A supporting web comprising an endless rubber belt engages both slave rolls. A disposable endless zinc oxide paper slave belt is placed over the supporting web. A corona charging device is situated above the slave belt and is energized from a high potential source of opposite polarity to that of the conventional corona charging device situated above the zinc oxide paper feed roll. The slave belt and its corona charging device are optically isolated from the zinc oxide paper feed roll and its corona charging device by barrier shields to prevent interaction and/r dissipation of the opposite charges imposed upon the zinc oxide paper on the feed roll and that on the slave belt. The development station is extended to enable developer to contact the slave belt. With these modifications, the copier is otherwise operated in conventional manner employing the developer system defined in example 2. The zinc oxide paper feed roll is employed in conventional manner for reproduction purposes whereas the slave belt continuously selectively removes grit from the developer. At any convenient time, such as when the zinc oxide paper feed roll is exhausted and must be replaced, the zinc oxide paper slave belt containing the accumulated grit can be discarded and replaced. Operating in this manner, the grit level remains below 1 percent up to 70,000 copies.

Although specific materials and conditions were set forth in the above exemplary processes of this invention, there are merely intended as illustrations of the present invention. Various other toners, carrier cores, substituents and processes such as those listed above may be substituted in the examples with similar results.

Other modifications of the present invention will occur to those skilled in the art upon a reading of the present disclosure. These are intended to be included within the scope of this invention.

What is claimed is:

1. Process for electrostatographic reproduction with continuous removal of grit from the developer comprising:

a. electrostatically charging the major portion of an electrostatographic imaging surface with a charge of first polarity and at least one terminal portion of said imaging surface with a charge of relatively opposite polarity to that being imposed upon said major portion of said surface;

b. imaging the major portion of said imaging surface to impart a latent electrostatic image thereto while substantially precluding the charge on said terminal portion of said imaging surface from being discharged; and bringing developer into contact with the entire imaging surface whereby the latent image on the major portion of said surface is developed and grit is selectively attracted to said terminal portion of said surface.

2. Process for electrostatographic reproduction as defined in claim 1 wherein both terminal portions of the imaging sur' face are charged with a charge of relatively opposite polarity to that being imposed upon the major portion of said imaging surface.

3. Process for electrostatographic reproduction as defined in claim 1 wherein the charge on said terminal portion or portions of the imaging surface is substantially precluded from being discharged by shielding said terminal portion or portions of said surface from said major portion of said imaging surface.

4. Process for electrostatographic reproduction as defined in Claim 1 wherein the terminal portion of said imaging surface is a slave roll having a photoresponsive surface.

5. Process for electrostatographic reproduction as defined in Claim 4 wherein the slave roll rotates at a speed of from about 10 percent to about 50 percent of the speed of rotation of the imaging surface.

6. Process for electorstatographic reproduction as defined in claim 3 wherein the shielding between the major and terminal portions of the imaging surface is present during at least the charging and imaging operations.

7. Process for electrostatographic reproduction as defined in claim 1 wherein the developed image is transferred to a support web and the entire imaging surface is cleaned thereby removing the attracted grit and any developer remaining on the imaging surface.

8. Process for electrostatographic reproduction as defined in claim 7 wherein after transferring said developed image to a support web, the imaging surface is precleaned by charging the major portion of the imaging surface with a charge of relatively opposite polarity to that initially imposed thereon and charging at least one terminal portion of said surface with a charge of relatively opposite polarity to that initially imposed thereon, thereby substantially neutralizing the charges on said imaging surface whereby the attracted grit and developer are substantially loosened from said surface.

9. Process for electrostatographic reproduction as defined in claim 8 wherein the loosened grit and developer are removed from the imaging surface by brushing said surface, and thereafter exposing said surface to light to dissipate any residual charge.

10. Process for electrostatographic reproduction with continuous removal of grit from the developer comprising:

a. electrostatically charging the major portion of an electrostatographic imaging surface with a charge of first polarity and at least one tenninal portion of said imaging surface with a charge of relatively opposite polarity to that being imposed upon said major portion of said surface;

b. imaging the major portion of said imaging surface to impart a latent electrostatic image thereto while substantially precluding the charge on said terminal portion of said surface from being discharged;

c. cascading developer across the entire photoresponsive surface whereby the latent image on the major portion of said surface is developed and grit is selectively attracted to said terminal portion of said surface; and

d. slitting and discarding the terminal portions of said imaging surface and recovering the developed image on the major portion of said surface.

11. In an electrostatographic reproducing apparatus, an improvement for continuous grit removal is provided comprismg:

i) an electrostatographic imaging surface;

ii) at least two corona discharge electrodes spaced from said surface and extending transversely across said surface; a first corona discharge electrode extending across a major portion of said imaging surface and adapted to impose a charge upon said portion of said surface; at least one additional corona discharge electrode extending across at least one terminal portion of said surface and adapted to impose a charge thereon of relatively opposite polarity to that imposed by said first electrode;

iii) at least one shielding member affixed to a frame element of the electrostatographic reproducing apparatus adapted to segregate said major and terminal portions of said imaging surface with respect to incident light and electrostatic charge;

iv) means for imaging the charged major portion of said imaging surface to impart a latent electrostatic image thereto;

v) means for cascading developer across the entire imaging surface, whereby the latent image is developed on the major portion of the surface and grit is selectively attracted to at least one terminal portion thereof; and

vi) means for recovering said developer upon completion of its traverse of the imaging surface;

vii) means for discarding the attracted grit; and

viii) means for recovering the developed image.

12. In an electrostatographic reproducing apparatus, an improvement for continuous grit removal is provided comprising:

i) an electrostatographic imaging surface;

ii) at least two corona discharge electrodes spaced from said surface and extending transversely across said surface; a first corona discharge electrode extending across a major portion of said imaging surface and adapted to impose a charge upon said portion of said surface; at least one additional corona discharge electrode extending across at least one terminal portion of said imaging surface and adapted to impose a charge thereon of relatively opposite polarity to that imposed by said first electrode;

iii) at least one shielding member affixed to a frame element of the electrostatographic reproducing apparatus adapted to segregate said major and terminal portions of said imaging surface with respect to incident light and electrostatic charge;

iv) means for imaging the charged major portion of said imaging surface to impart a latent electrostatic image thereto;

v) means for cascading developer across the entire imaging surface whereby the latent image is developed on the major portion of the surface and grit is selectively attracted to at least one terminal portion thereof;

vi) means for recovering said developer upon completion of its traverse of the imaging surface; and

vii) means for separating at least one terminal portion of the imaging surface from the major portion thereof to remove the attracted grit; and

viii) means for recovering the developed image.

LII

13. In an electrostatographic reproducing apparatus, an im provement for continuous grit removal is provided comprismg:

i) an electrostatographic imaging surface in the shape of a drum journaled for rotation about a horizontal axis in a frame element of the electrostatographic reproducing apparatus;

ii) at least two corona discharge electrodes spaced from said drum and extending transversely across the drum surface; a first corona discharge electrode extending across a major portion of said drum surface and adapted to impose a charge upon said portion of said drum surface; at least one additional corona discharge electrode extending across at least one terminal portion of said drum surface and adapted to impose a charge thereon of relatively opposite polarity to that imposed by said first electrode;

iii) at least one shielding member affixed to a frame element of the electrostatographic reproducing apparatus adapted to segregate said major and terminal portions of said drum with respect to incident light and electrostatic charge;

iv) means for imaging the charged major portion of said drum to impart a latent electrostatic image thereto;

v) means for cascading developer across the entire surface of said drum whereby the latent image on the major portion of said drum is developed and the grit is selectively attracted to at least one terminal portion thereof;

vi) means for recovering said developer upon completion of its traverse of the drum surface;

vii) means for transferring said developed image to a support material; and

viii) means for cleaning the entire surface of said drum to remove attracted grit and any residual developer therefrom.

14. An electrostatographic reproducing apparatus as defined in claim 13 wherein a first corona discharge electrode extends across a major portion of the drum surface adapted to impose a charge upon said portion of said surface; and two additional corona discharge electrodes; each electrode extending across a terminal portion of said drum and adapted to impose a charge thereon of relatively opposite polarity to that imposed by said first electrode.

15. An electrostatographic reproducing apparatus as defined in claim 14 wherein shielding members affixed to a frame element of said apparatus are adapted to segregate each of said terminal portions of the drum from the major portion thereof with respect to incident light and electrostatic charge.

16. An electrostatographic reproducing apparatus as defined in claim 13 wherein at least one shielding member extends through the charging and imaging zones.

17. An electrostatographic reproducing apparatus as defined in claim 13 wherein a brush adapted to rotate extends across the entire surface of the drum in contact therewith and adapted to clean the entire surface of the drum to remove attracted grit and any residual developer therefrom.

18. An electrostatographic reproducing apparatus as defined in claim 13 wherein the means for cleaning the drum surface comprises at least two corona discharge electrodes spaced from and extending transversely across said drum; the first corona discharge electrode extending across a major portion of said drum and adapted to impose a charge of relatively opposite polarity to that initially imposed on said portion of the drum; at least one additional corona discharge electrode extending across at least one terminal portion of said drum and adapted to impose a charge of relatively opposite polarity to that initially imposed on said portion of the drum; whereby the attracted grit and any residual developer is loosened from said drum; a brush adapted to rotate in contact with said drum surface to remove said loosened grit and developer, and a discharge lamp adapted to dissipate any residual charge on said drum.

19. In an electrostatographic reproducing apparatus, an improvement for continuous grit removal is provided comprismg:

i) an electrostatographic imaging surface in the shape of a drum mounted on a shaft, journaled for rotation about a horizontal axis in a frame element of the reproducing apparatus;

ii) at least one slave roll mounted on said shaft adjacent the imaging drum, said slave roll having a photoresponsive surface;

iii) a first corona discharge electrode spaced from said imaging drum and extending transversely across the surface thereof, and first electrode adapted to impose a charge upon the surface of said imaging drum;

iv) at least one additional corona discharge electrode spaced from at least one slave roll and extending transversely across the surface thereof, said electrode adapted to impose a charge upon the surface of said slave roll of relatively opposite polarity to that imposed by said first electrode;

v) at least one shielding member affixed to a frame element of the reproducing apparatus adapted to segregate said imaging drum and said slave roll with respect to incident light and electrostatic charge;

vi) means for imaging the charged imaging surface of the imaging drum to impart a latent electrostatic image thereto;

vii) means for cascading developer across the respective surfaces of the imaging drum and at least one slave roll whereby the latent image on the imaging drum is developed and the grit is selectively attracted to at least one slave roll;

viii) means for recovering said developer upon completion of its traverse of the imaging drum and slave roll surfaces;

ix) means for transferring said developed image to a support material; and

it) means for cleaning the surfaces of the imaging drum and slave roll to remove attracted grit and any residual developer therefrom.

20. Apparatus as defined in claim 19 wherein the slave roll is mounted on said shaft through a gear train adapted to reduce the speed of rotation of said slave roll relative to the imaging drum.

21. In an electrostatographic reproducing apparatus, an improvement for continuous grit removal is provided comprismg:

i) an electrostatographic imaging surface in the shape of a feed roll mounted on a shaft journaled for rotation about L6 a horizontal axis in a frame element of the reproducing apparatus;

ii) a drum mounted on a shaft journaled for rotation about a horizontal axis, said drum spaced from said electrostatographic feed roll. and in the same horizontal plane, said drum being adapted to receive the electrostatographic imaging surface and transport said surface through a development zone;

iii) at least one slave roll mounted on the shaft bearing the feed roll adjacent at least one terminal position thereof; v) at least one additional slave roll mounted on the shaft bearing the drum adjacent at least one terminal portion thereof;

v) at least one endless belt having a photoresponsive surface adapted to engage the slave rolls on both the feed roll and drum shafts to produce rotation of said belt;

vi) a first corona discharge electrode spaced from said feed roll and extending transversely across the surface thereof, said first electrode adapted to impose a charge upon the electrostatographic imaging surface of said feed roll;

vii) at least one additional corona discharge electrode spaced from at least one endless belt and extending transversely across the surface thereof, said electrode adapted to impose a charge upon the surface of said belt of relatively opposite polarity to that imposed by said first electrode;

viii) at least one shielding member affixed to a frame element of the reproducing apparatus adapted to segregate said feed roll and said endless belt with respect to lnCl ent light and electrostatic charge;

ix) means for imaging the charged imaging surface of the feed roll to impart a latent electrostatic image thereto;

x) means for cascading developer across the respective surfaces of the feed roll and endless belt, whereby the latent image on the feed roll is developed and the grit is selectively attracted to at least one endless belt;

xi) means for recovering said developer upon completion of its traverse of the feed roll and endless belt surfaces;

xii) means for discharging the developed copy; and

xiii) means enabling periodic replacement of said endless belt.

22. Apparatus as defined in claim 21 wherein the slave roll is mounted on the shaft bearing the feed roll through a gear train adapted to reduce the speed of rotation of said slave roll relative to the feed roll. 

1. Process for electrostatographic reproduction with continuous removal of grit from the developer comprising: a. electrostatically charging the major portion of an electrostatographic imaging surface with a charge of first polarity and at least one terminal portion of said imaging surface with a charge of relatively opposite polarity to that being imposed upon said major portion of said surface; b. imaging the major portion of said imaging surface to impart a latent electrostatic image thereto while substantially precluding the charge on said terminal portion of said imaging surface from being discharged; and c. bringing developer into contact with the entire imaging surface whereby the latent image on the major portion of said surface is developed and grit is selectively attracted to said terminal portion of said surface.
 2. Process for electrostatographic reproduction as defined in claim 1 wherein both terminal portions of the imaging surface are charged with a charge of relatively opposite polarity to that being imposed upon the major portion of said imaging surface.
 3. Process for electrostatographic reproduction as defined in claim 1 wherein the charge on said terminal portion or portions of the imaging surface is substantially precluded from being discharged by shielding said terminal portion or portions of said surface from said major portion of said imaging surface.
 4. Process for electrostatographic reproduction as defined in Claim 1 wherein the terminal portion of said imaging surface is a slave roll having a photoresponsive surface.
 5. Process for electrostatographic reproduction as defined in Claim 4 wherein the slave roll rotates at a speed of from about 10 percent to about 50 percent of the speed of rotation of the imaging surface.
 6. Process for electorstatographic reproduction as defined in claim 3 wherein the shielding between the major and terminal portions of the imaging surface is present during at least the charging and imaging operations.
 7. Process for electrostatographic reproduction as defined in claim 1 wherein the developed image is transferred to a support web and the entire imaging surface is cleaned thereby removing the attracted grit and any developer remaining on the imaging surface.
 8. Process for electrostatographic reproduction as defined in claim 7 wherein after transferring said developed image to a support web, the imaging surface is precleaned by charging the major portion of the imaging surface with a charge of relatively opposite polarity to that initially imposed thereon and charging at least one terminal portion of said surface with a charge of relatively opposite polarity to that initially imposed thereon, thereby substantially neutralizing the charges on said imaging surface whereby the attracted grit and developer are substantially loosened from said surface.
 9. Process for electrostatographic reproduction as defined in claim 8 wherein the loosened grit and developer are removed from the imaging surface by brushing said surface, and thereafter exposing said surface to light to dissipate any residual charge.
 10. Process for electrostatographic reproduction with continuous removal of grit from the developer comprising: a. electrostatically charging the major portion of an electrostatographic imaging surface with a charge of first polarity and at least one terminal portion of said imaging surface with a charge of relAtively opposite polarity to that being imposed upon said major portion of said surface; b. imaging the major portion of said imaging surface to impart a latent electrostatic image thereto while substantially precluding the charge on said terminal portion of said surface from being discharged; c. cascading developer across the entire photoresponsive surface whereby the latent image on the major portion of said surface is developed and grit is selectively attracted to said terminal portion of said surface; and d. slitting and discarding the terminal portions of said imaging surface and recovering the developed image on the major portion of said surface.
 11. In an electrostatographic reproducing apparatus, an improvement for continuous grit removal is provided comprising: i) an electrostatographic imaging surface; ii) at least two corona discharge electrodes spaced from said surface and extending transversely across said surface; a first corona discharge electrode extending across a major portion of said imaging surface and adapted to impose a charge upon said portion of said surface; at least one additional corona discharge electrode extending across at least one terminal portion of said surface and adapted to impose a charge thereon of relatively opposite polarity to that imposed by said first electrode; iii) at least one shielding member affixed to a frame element of the electrostatographic reproducing apparatus adapted to segregate said major and terminal portions of said imaging surface with respect to incident light and electrostatic charge; iv) means for imaging the charged major portion of said imaging surface to impart a latent electrostatic image thereto; v) means for cascading developer across the entire imaging surface, whereby the latent image is developed on the major portion of the surface and grit is selectively attracted to at least one terminal portion thereof; and vi) means for recovering said developer upon completion of its traverse of the imaging surface; vii) means for discarding the attracted grit; and viii) means for recovering the developed image.
 12. In an electrostatographic reproducing apparatus, an improvement for continuous grit removal is provided comprising: i) an electrostatographic imaging surface; ii) at least two corona discharge electrodes spaced from said surface and extending transversely across said surface; a first corona discharge electrode extending across a major portion of said imaging surface and adapted to impose a charge upon said portion of said surface; at least one additional corona discharge electrode extending across at least one terminal portion of said imaging surface and adapted to impose a charge thereon of relatively opposite polarity to that imposed by said first electrode; iii) at least one shielding member affixed to a frame element of the electrostatographic reproducing apparatus adapted to segregate said major and terminal portions of said imaging surface with respect to incident light and electrostatic charge; iv) means for imaging the charged major portion of said imaging surface to impart a latent electrostatic image thereto; v) means for cascading developer across the entire imaging surface whereby the latent image is developed on the major portion of the surface and grit is selectively attracted to at least one terminal portion thereof; vi) means for recovering said developer upon completion of its traverse of the imaging surface; and vii) means for separating at least one terminal portion of the imaging surface from the major portion thereof to remove the attracted grit; and viii) means for recovering the developed image.
 13. In an electrostatographic reproducing apparatus, an improvement for continuous grit removal is provided comprising: i) an electrostatographic imaging surface in the shape of a drum journaled for rotation about a horizontal axis in a frame element of the electrostatographic reproducing Apparatus; ii) at least two corona discharge electrodes spaced from said drum and extending transversely across the drum surface; a first corona discharge electrode extending across a major portion of said drum surface and adapted to impose a charge upon said portion of said drum surface; at least one additional corona discharge electrode extending across at least one terminal portion of said drum surface and adapted to impose a charge thereon of relatively opposite polarity to that imposed by said first electrode; iii) at least one shielding member affixed to a frame element of the electrostatographic reproducing apparatus adapted to segregate said major and terminal portions of said drum with respect to incident light and electrostatic charge; iv) means for imaging the charged major portion of said drum to impart a latent electrostatic image thereto; v) means for cascading developer across the entire surface of said drum whereby the latent image on the major portion of said drum is developed and the grit is selectively attracted to at least one terminal portion thereof; vi) means for recovering said developer upon completion of its traverse of the drum surface; vii) means for transferring said developed image to a support material; and viii) means for cleaning the entire surface of said drum to remove attracted grit and any residual developer therefrom.
 14. An electrostatographic reproducing apparatus as defined in claim 13 wherein a first corona discharge electrode extends across a major portion of the drum surface adapted to impose a charge upon said portion of said surface; and two additional corona discharge electrodes; each electrode extending across a terminal portion of said drum and adapted to impose a charge thereon of relatively opposite polarity to that imposed by said first electrode.
 15. An electrostatographic reproducing apparatus as defined in claim 14 wherein shielding members affixed to a frame element of said apparatus are adapted to segregate each of said terminal portions of the drum from the major portion thereof with respect to incident light and electrostatic charge.
 16. An electrostatographic reproducing apparatus as defined in claim 13 wherein at least one shielding member extends through the charging and imaging zones.
 17. An electrostatographic reproducing apparatus as defined in claim 13 wherein a brush adapted to rotate extends across the entire surface of the drum in contact therewith and adapted to clean the entire surface of the drum to remove attracted grit and any residual developer therefrom.
 18. An electrostatographic reproducing apparatus as defined in claim 13 wherein the means for cleaning the drum surface comprises at least two corona discharge electrodes spaced from and extending transversely across said drum; the first corona discharge electrode extending across a major portion of said drum and adapted to impose a charge of relatively opposite polarity to that initially imposed on said portion of the drum; at least one additional corona discharge electrode extending across at least one terminal portion of said drum and adapted to impose a charge of relatively opposite polarity to that initially imposed on said portion of the drum; whereby the attracted grit and any residual developer is loosened from said drum; a brush adapted to rotate in contact with said drum surface to remove said loosened grit and developer, and a discharge lamp adapted to dissipate any residual charge on said drum.
 19. In an electrostatographic reproducing apparatus, an improvement for continuous grit removal is provided comprising: i) an electrostatographic imaging surface in the shape of a drum mounted on a shaft, journaled for rotation about a horizontal axis in a frame element of the reproducing apparatus; ii) at least one slave roll mounted on said shaft adjacent the imaging drum, said slave roll having a photoresponsive surface; iii) a first corona discharge electrode spaced from said imaging Drum and extending transversely across the surface thereof, and first electrode adapted to impose a charge upon the surface of said imaging drum; iv) at least one additional corona discharge electrode spaced from at least one slave roll and extending transversely across the surface thereof, said electrode adapted to impose a charge upon the surface of said slave roll of relatively opposite polarity to that imposed by said first electrode; v) at least one shielding member affixed to a frame element of the reproducing apparatus adapted to segregate said imaging drum and said slave roll with respect to incident light and electrostatic charge; vi) means for imaging the charged imaging surface of the imaging drum to impart a latent electrostatic image thereto; vii) means for cascading developer across the respective surfaces of the imaging drum and at least one slave roll whereby the latent image on the imaging drum is developed and the grit is selectively attracted to at least one slave roll; viii) means for recovering said developer upon completion of its traverse of the imaging drum and slave roll surfaces; ix) means for transferring said developed image to a support material; and x) means for cleaning the surfaces of the imaging drum and slave roll to remove attracted grit and any residual developer therefrom.
 20. Apparatus as defined in claim 19 wherein the slave roll is mounted on said shaft through a gear train adapted to reduce the speed of rotation of said slave roll relative to the imaging drum.
 21. In an electrostatographic reproducing apparatus, an improvement for continuous grit removal is provided comprising: i) an electrostatographic imaging surface in the shape of a feed roll mounted on a shaft journaled for rotation about a horizontal axis in a frame element of the reproducing apparatus; ii) a drum mounted on a shaft journaled for rotation about a horizontal axis, said drum spaced from said electrostatographic feed roll and in the same horizontal plane, said drum being adapted to receive the electrostatographic imaging surface and transport said surface through a development zone; iii) at least one slave roll mounted on the shaft bearing the feed roll adjacent at least one terminal position thereof; v) at least one additional slave roll mounted on the shaft bearing the drum adjacent at least one terminal portion thereof; v) at least one endless belt having a photoresponsive surface adapted to engage the slave rolls on both the feed roll and drum shafts to produce rotation of said belt; vi) a first corona discharge electrode spaced from said feed roll and extending transversely across the surface thereof, said first electrode adapted to impose a charge upon the electrostatographic imaging surface of said feed roll; vii) at least one additional corona discharge electrode spaced from at least one endless belt and extending transversely across the surface thereof, said electrode adapted to impose a charge upon the surface of said belt of relatively opposite polarity to that imposed by said first electrode; viii) at least one shielding member affixed to a frame element of the reproducing apparatus adapted to segregate said feed roll and said endless belt with respect to incident light and electrostatic charge; ix) means for imaging the charged imaging surface of the feed roll to impart a latent electrostatic image thereto; x) means for cascading developer across the respective surfaces of the feed roll and endless belt, whereby the latent image on the feed roll is developed and the grit is selectively attracted to at least one endless belt; xi) means for recovering said developer upon completion of its traverse of the feed roll and endless belt surfaces; xii) means for discharging the developed copy; and xiii) means enabling periodic replacement of said endless belt.
 22. Apparatus as defined in claim 21 wherein the slave roll is mounted on the shaft bearing thE feed roll through a gear train adapted to reduce the speed of rotation of said slave roll relative to the feed roll. 